The maximally attainable V̇o2during exercise in humans: the peak vs. maximum issue

Abstract

The quantification of maximum oxygen uptake (V̇o 2 max), a parameter characterizing the effective integration of the neural, cardiopulmonary, and metabolic systems, requires oxygen uptake (V̇o 2) to attain a plateau. We were interested in whether a V̇o 2 plateau was consistently manifest during maximal incremental ramp cycle ergometry and also in ascertaining the relationship between this peak V̇o 2(V̇o 2 peak) and that determined from one, or several, maximal constant-load tests. Ventilatory and pulmonary gas-exchange variables were measured breath by breath with a turbine and mass spectrometer. On average, V̇o 2 peak[3.51 ± 0.8 (SD) l/min] for the ramp test did not differ from that extrapolated from the linear phase of the response in 71 subjects. In 12 of these subjects, the V̇o 2 peak was less than the extrapolated value by 0.1-0.4 l/min (i.e., a “plateau”), and in 19 subjects, V̇o 2 peak was higher by 0.05-0.4 l/min. In the remaining 40 subjects, we could not discriminate a difference. The V̇o 2 peak from the incremental test also did not differ from that of a single maximum constant-load test in 38 subjects or from the V̇o 2 max in 6 subjects who undertook a range of progressively greater discontinuous constant-load tests. A plateau in the actual V̇o 2 response is therefore not an obligatory consequence of incremental exercise. Because the peak value attained was not different from the plateau in the plot of V̇o 2 vs. work rate (for the constant-load tests), the V̇o 2 peak attained on a maximum-effort incremental test is likely to be a valid index of V̇o 2 max, despite no evidence of a plateau in the data themselves. However, without additional tests, one cannot be certain.